Method of placing a well on production

ABSTRACT

A method for removing liquid from a natural-flow well so as to reduce the hydrostatic pressure in the well below the formation pressure so that formation fluids will flow from the formation into the well and through the well to the surface. At least one slug of compressed gas is injected into the well annulus thereby displacing some of the liquid in the annulus into the tubing and forcing liquid in the tubing upward and out of the tubing. A volume of foaming agent solution is then injected into the annulus, displacing more liquid from the annulus into the tubing and forcing liquid in the tubing upward. Pressure on the annulus is then released, causing foam to form in the well. In this manner the hydrostatic pressure of liquid in the well is reduced below the formation pressure so that fluid can flow from the formation into the well.

Bernard Aug;7,1973

[ METHOD OF PLACING A WELL ON PRODUCTION [75] Inventor: George G.Bernard, La Mirada,

Calif.

[73] Assignee: Union Oil Company of California,

Los Angeles, Calif.

22 Filed: May 3, 1912 211 Appl. No.: 249,820

Cornelius 166/309 X Hutchison et al 166/314 X Primary Examiner-StephenJ. Novosad AttorneyMilton W. Lee, Dean Sandford et al.

[57] ABSTRACT A method for removing liquid from a natural-flow well soas to reduce the hydrostatic pressure in the well below the formationpressure so that formation fluids will flow from the formation into thewell and through the well to the surface. At least one slug ofcompressed gas is injected into the well annulus thereby displacing someof the liquid in the annulus into the tubing and forcing liquid in thetubing upward and out of the tubing. A volume of foaming agent solutionis then injected into the annulus, displacing more liquid from theannulus into the tubing and forcing liquid in the tubing upward.Pressure on the annulus is then released, causing foam to form in thewell. In this manner the hydrostatic pressure of liquid in the well isreduced below the formation pressure so that fluid can flow from theformation into the well.

10 Claims, 6 Drawing Figures PAIENIEM SHEEI 1 0f 3 re 1014 PRESSURE :526 RIHIIIH Ti 2 a .23 i in! I \\JY\ METHOD OFPLACING A WELL ONPRODUCTION This invention relates to the production of oil and/or gasfrom subterranean fluid-bearing formations, and more particularlyconcerns a method forinitiating production of oil and/or gas through awell penetrating a fluid-bearing subterranean formation wherein thepressure in the formation is sufficient to cause the produced fluids toflow from the formation to the surface, but is insufficient to overcomethe hydrostatic head of a column of liquid in the well.

It is conventional practice in the drilling of wells into subterraneanfluid-bearing strata, and in the completion, workover and treatment ofsuch wells to maintain a column of liquid in the well of sufficientdensity to overcome the fomration pressure, thereby preventing blowoutof the well during the contemplated operation. In many oil and/or gasproducing operations, the pressure in the formation is sufficient tocause the produced fluids to flow naturally from the formation to thesurface without pumping or other externally induced lifting, but isinsufficient to overcome the hydrostatic head of the column of drillingmud, completion fluid, or other liquid in the well. Thus, it becomesnecessary to remove at least a portion of the liquid from the well so asto reduce the hydrostatic pressure in the well adjacent to the producingformation sufficiently to permit the flow of produced fluids into thewell and through the well to the surface.

The removal of liquid from the well has conventionally been accomplishedby swabbing the well, i.e., by

running a special swabbing tool into the well on a wire line tomechanically lift liquid out of the well. The swabbing operationrequires the expense of bringing special equipment to the well, and theswabbing action itself often requires several days to carry out. Whenthe drilling is carried out at a remote, inaccessible location, forexample, in the Arctic or in the tropics, where transportation isdifficult, the expense of bringing in special equipment and of operatingit can be prohibitive.

It has been proposed, for example in US. Pat. No. 3,019,839 to Bloom, torelieve the hydrostatic pressure of fluids in a well by application ofgas pressure alternately to the liquid within the tubing and to that inthe annulus in order to force this liquid tothesurface and out of thewell. By repeatedly applying gas pressure alternately to the liquid inthe tubing and in the annulus, a pendulum-like or rocking action ofliquid witin the annulus and the tubing is induced and liquid isdischarged through both the tubing and annulus until thehydrostatiepressure is lowered sufficiently to allow recovery of the oilfrom the well by natural flow or by pumping. While theoreticallyattractive, this alternate application of gas to the annulus and thetubing requires a high pressure compressor to supply gas at a pressuresufficient to overcome a substantial hydrostatic head so as to displaceliquid from the wells, e.g., nitrogen at pressure of 1,000 to 5,000 psiand higher, and also requires expensive, quickly responsive valves toswitch the flow of this high pressure gas alternately to the tubing andto the annulus. Accordingly, use of this method is limited to the moreaccessible sites where such equipment is more readily available.

Recently, it has been suggested that production of gas from gas wellscan be stimulated by dropping surfactants, preferably in stick form,into the tubing string to. induce foaming in the well. These foam sticksde-' pend fortheir activity upon gas produced by the well and are of useonly where the well is producing gas; if

the well does not produce a significant quantity of gas, the foam sticksare allbut useless. f

U.S. Pat. No. 2,168,116 to Crites et al. sets forth a method whichinvolves the creation of a controlled foam lift condition in order toinduce flow of oil wells. In accordance with this method, afoaming agentis added to the oil in the well with the producing column closed off.Next, the liquid and foaming agent in the well is agitated by theinjection of gas under pressure; and the producing column is then openedto allow the well to flow under its own pressure. This method alsorequires the use of an expensive high pressure compres sor to assurethat gas is supplied to the bottom of the borehole in an amountsufficient 0t provide the agitation necessary to form foam.

A need therefore exists for a simple, yet effective method forinitiating production from a natural-flow well in which the hydrostaticpressure of liquid in the well prevents the flow of produced fluids fromthe formation to the well. This method should make use only of equipmentnormally present at oil field sites and require no specialized orexpensive equipment.

Accordingly, a primary object of this invention is to provide a simplemethod for initiating the production of oil and/or gas from afluid-bearing subterranean formation penetrated by a well.

Another object of this invention is to provide a simple,inexpensivemethod for removing liquid from a well.

Still another object of this invention is toprovide a method forinitiating the production of fluids from a fluid-bearing formationhaving sufficient pressure to causethe produced fluids to flow naturallyfrom the formation to the surface without pumping or other externallyinduced lifting, but insufficient pressure to overcome the hydrostatichead of a column of liquid in the well.

Yet another object of this invention is to provide a simple, inexpensivemethod for initiating the production of oil and/or gas from afluid-bearing subterranean formation which does not require specializedequipment.

These and other objects and advantages of the invention will be apparentfrom the following detailed description.

According to this invention, quiescent liquids are removed from a wellto reduce the hydrostatic pressure .in the well by injecting at leastone slug of compressed gas into the annulus between the walls of thewell and the production tubing, with the tubing open, thereby displacingsome of the liquid in the annulus from the annulus into the tubingandforcing'liquid in the tubing upward and into a low pressure receiverlocated at the surface. The tubing is kept open and pressure maintainedin the annulus while a measured volume of a foaming agent solution isinjectedinto the annulus, thereby compressing the previously injectedgas and displacing still more fluid in the annulus from the annulus intothe tubing and forcing liquid in the tubing into the low pressurereceiver. The pressure on the annulus is then reduced. With thereduction in pressure, foam is produced in the annulus, thereby loweringthe density of the fluid in the annulus wherebyfluid in the annulusflows into a low pressure receiver at the surface and liquid flows fromthe tubing into the annulus. Wlth 3 the removal of liquid from thetubing and annulus, the hydrostatic pressure in the well is loweredsufficiently that fluids will flow from the formation into the well.

In embodiments of this invention particularly preferred for use indifficulty accessible locations where only limited equipment isavailable, the compressed slug of gas can be provided from a lowpresusre compressor, i.e., one having an output of only about 60 to 150psig. The gas output of such compressor is admitted into a closed gasstorage vessel and water then introduced into, i.e., pumped into, thevessel to compress the gas therein to a higher pressure, i.e., to about500 to 1,500 psig.

The invention is further defined by the accompanying drawings, whereinlike numerals refer to like parts throughout, and in which:

FIG. I is a schematic cross sectional view of a well completed in apermeable subterranean reservoir illustrating the condition of the wellat the time when the process of this invention is to be initiated anddepicting means which can be employed in practicing the invention;

FIG. 2 is a schematic cross sectional view of the well illustrating thefirst step of this invention wherein a slug of gas under pressure isintroduced into the annulus;

FIG. 3 is a schematic cross sectional view of the well illustrating thesecond step of the process of this invention in which foaming agentsolution is injected into the annulus;

FIG. 4 is a schematic cross sectional view of the well illustrating thecondition after the third step of the treatment in which the pressure inthe annulus is reduced and foam formed therein;

FIG. 5 is a vertical cross sectional view of the well illustrating thelevel of fluids in the well after completion of the process of thisinvention and after the flow of fluids from the formation isestablished; and

FIG. 6 is a schematic illustration of the apparatus used to adapt a lowpressure compressor for the practice of the method of this invention.

Referring now particularly to FIG. 1, a well 10 is shown traversing apermeable fluid-bearing formation 12, which is shown bounded at itsupper and lower extremities by essentially impermeable strata 14 and 16,respectively, strata 14 being overlain by the formation 18. Theillustrated well is cased and cemented through formations 12, 14 and 18with casing 20 which is surrounded by an outer cement sheath 22. Casing20 and cement sheath 22 are perforated at a plurality of locations 24thereby providing fluid communication be tween the interior of thecasing and formation 12. Tubing 26, which can be a conventionalproduction tubing or simply a length of tubing lowered into the well,extends from the surface downwardly into well 10, preferablysubstantially coaxially within casing 20. Although the well is shown inthis embodiment as cased, it is to be understood that the method of thisinvention is amenable to practice in both cased and uncased wells and inwells completed with conventional slotted liners.

Annulus 28 is formed between tubing 26 and the inner wall of casing 20.The bottom of tubing 26 is spaced from the bottom of the well so thatthere is fluid communication between annulus 28 and the interior oftubing 26. A column of liquid 30, which can be, for example, residualfluids from the drilling operation, has accumulated in tubing 26 and acorresponding column of liquid 32 in the annulus 28. The hydrostaticpressure exerted by these fluids in the well adjacent to fluidbearingformation 12 exceeds the formation pressure so that fluids are preventedfrom flowing from the formation into the well. It is the purpose of thisinvention to depress the level of these fluids in the well by removingat least a portion thereof in order to reduce the hydrostatic pressurein the well sufficiently to allow fluid to flow from the formation intothe well.

Tubing 26 extends through gas tight cap 34 which closes the upper end ofthe casing, a gas-tight seal being provided at the juncture of tubing 26and cap 34. Valve 36 regulates the flow of fluid through tubing 26.Conduit 38 extends between compressor 40 and casing 20, and providesmeans by which gas under pressure can be conducted from compressor 40 toannulus 28, and conduit 47 provides means for communicating annulus 28with the low pressure receiver. Valve 48 regulates the flow of gasthrough conduit 38 and valve 49 regulates flow from the annulus 28 tothe low pressure receiver. Conduit 42 communicates annulus 28 and asupply source 46, which contains an aqueous solution of foaming agent.Flow of fluid through conduit 42 is regulated by valve 44.

In accordancewith this invention and as particularly illustrated in FIG.2, a slug of compressed gas is admitted into annulus 28 compressor 40 byopening valve 48. The gas introduced into annulus 28 displaces liquidfrom the annulus into tubing 26 and thence upwardly through tubing 26 toa low pressure receiver such as a sump or tank, not shown, located atthe surface. The level of the liquid in annulus 28 is depressed to alower level 50. Valve 36 which regulates flow in the tubing, is open sothat liquid displaced from the well flows from tubing 26 to the lowpressure receiver. This stepcan be repeated a plurality of times,setting up a rocking action within the well, with more liquid beingexpelled from tubing 26 as each slug of compressed gas is admitted intoannulus 28.

After the column of liquid in the annulus has been depressed to thelower level 50, a metered volume of foaming agent is introduced into theannulus from supply source 46 by opening valve 44. The foaming agentsolution can be pressured or pumped into the annulus in conventionalmanner. As shown in FIG. 3, a column '42 of foaming agent solution isformed above a cushion 54 of compressed gas which in turn is abovecolumn 32 of liquid in the annulus. The presence of this cushion may bemomentary, with migration of foaming agent through the air cushionoccurring in a relatively short time period. However, in. some downholesituations, this air cushion can be present for a period of severalminutes up to an hour or so with only a relatively small quantity offoaming agent solution passing through the cushion. Pressure ismaintained on the annulus by maintaining valves 48 and 49 closed. Tubing26 is at this stage substantially filled with liquid, some of thisliquid overflowing the tubing and being displaced into the low pressurereceiver which is at substantially atmospheric pressure, the onlypressure upon the liquid in the tubing is that due to the hydraulic headof liquid in the tubing.

In FIG. 4, the condition of the well is shown after pressure on theannulus is released by opening valve 47. As illustrated in this FIGURE,a column of foam 60 is formed in annulus 28. At least a portion of thisfoam is dischargedfrom the annulus through conduit 47, and the densityof liquids remaining in the annulus is lowered as indicated by liquidinterface 62. Also, liquid flows from tubing 26 flow back into theannulus, so that tubing 26 is only partially filled with liquid 30, asindicated by the level ,64, thereby lowering the hydrostatic pressure inthe well adjacent to formation 12.

In FIG. 5, the well is shown with a lower level of liquid 32 in theannulus as illustrated by liquid interface 66. Some foam remains in theannulus, however, a portion has broken down or been dispelled therefrom.Also, gas will accumulate in the annulus, tending to depress the liquidtherein. With the hydrostatic pressure in the well lowered, normal flowof fluids from the formation to the well can occur. In the case of anaturally flowing well of the type illustrated, pressure within theformation will be sufficient to elevate oil and gas coming into the wellto the surface as rapidly as it is supplied to the well by theformation.

An estimation of the drop in the level of liquid in the wellin responseto injection of gas at a given known pressure and subsequent injectionof a given volume of foaming agent solution is given by the equations His the distance between the surface and the top of the liquid level 50in the well after injection of compressed gas;

H is the distance between the surface and the top of the liuqid level 56(bottom of air cushion) after injection of a volume (Vw) of foamingagent solution;

Vw is the volume of foaming agent solution injected into the annulus;

P is the pressure of gas in the annulusabove the liquidlevel afterinjection of the compressed gas (but before injection of the foamingagent solution);

P is the specific gravity of the aqueous solution of foaming agent,which usually. is approximately that of water; and i k is a constant;and

H: k Hz A) H is the distance between the surface and the top of theliquid level in the well immediately after the the depressurizationstep; i

H, is as determined in equation I),

A0 is the cross sectional area of the annulus;

A, is the cross sectional area of the tubing; and

k is a constant.

Knowing; the pressure and volumes of gas and of foaming agent solutionsavailable, the above equations can be used to determine the displacementof liquid in the well and, conversely, the requirements for achieving acertain amount of displacement. can be calculated. 3 v i I As indicatedabove, gas pressures used in the method of this invention are relativelylow, usually within the range of about 50 psitoabout 1,500 psi, and moreparticularly within-.the range fromiabout 500 psi to about l,200 psi.Since this pressure is exerted. in slugs on fluid in the annulus,,thereis,advantageously, no-needfor a powerful, high pressure compressor. Infield operations, especially at remote locations, pressures sufficientto initiate flow of fluids from the wellcan be generated using equipmentnormally present at a drilling site.

An alternative method of using a low pressure cornpressor in a, highpressure operation is illustrated in FIG. 6. This equipment comprises alow pressure compressor 70, e.g., one havingan output of about 70 toabout 150 psig. This small compressor is employed in conjunction with apump 72, for example, a mud circulation pump, and an air storage vessel74. In use, air

from low pressure compressor 70* at about 150 psig is admitted into theair storage vessel 74 and water pumped into the storage vessel from awater source, not shown, using pump 72 in order to compress the air inthe vessel 74, for example, to a pressure of about 500 to 1,500 psig.Air so compressed is then fed through conduit 43 into the annulus 28 ofthe well where it acts to force the liquid in the annulus downward,thereby displacing liquid from the annulus into the tubing and from thetubing intothe low'pressure receiver as shown in FIG. 2.

In some instances, only one slug of gas, such as air, exerted on theliquid in the annulus 28 can suffice. However, in preferred embodimentsof this invention, compressed gas is intermittently injected into theannulus aplurality of times, liquid being forced upward in the tubingeach time. Usually, for wells of about 3,000

to 7,500 feet depth in which there is calculated to be a moderateformation pressure, e.g., 2,800 to 4,400

psig, a slug of compressed gas will be injected into the annulus aboutthree to ten times before foaming agent solution is injected. Deeperwells with higher hydrostatic pressures of liquid therein and those inwhich the formation pressure is relativelylow can require the injectionof about 15 to 50 or more slugs of compressed gas. In cases where aplurality of slugs of compressed gas are required, each slug can beprovided using the apparatus of FIG. 6. Usually a total of about toabout 3,000 cubic feet of gas measured at injection temperature andpressure will be injected into the annulus.

Owing to economic considerations, the compressed gas employed willusually be air. However, the gas can be a hydrocarbon gas, e.g., naturalgas comprising mixtures of methane and ethane; any of the chemicallyinert gases, e.g., helium, argon,.or nitrogen carbon dioxide;and othergases which do not condense under the conditions employed or reactchemically to an appreciable extent with fluids in the annulus. It isdesir able that the gas employed be insoluble or only very 1 slightlysoluble in the liquid, but relatively high solubility should notpreclude the use of a particular gas. However, if a soluble gas is used,it is necessary to supply sufficient gas over and above that whichdissolves to insure that both liquid and gas phases exist in the well.

As indicated by the formula set forth above, the amount of liquiddisplaced from the well varies in pro porti'onto the volume of thefoaming agent and gas injected intothe well. Usually from about 250cubic feet" to about 3,000 cubic feet of foaming agent solution willsuffice inmost situations, this amount naturally varying inter alia withthe depth of the well itself, the depth of liquid in the well, thepressure of the gas injected prior to injection of the foaming agentsolution, and the dimensions of the tubing and casing.

When the foaming agent is injected into the annulus of the well abovethe cushion previously established by the compressed gas, additionalliquid is displaced from annulus 28 into tubing 26 and thence into thelow pressure receiver. Releasing pressure in the annulus, e.g., byopening valve 49, allows the compressed gas in the air cushion to expandand to rise in the annulus. Contact of the expanding gas with thefoaming agent causes a foam to be formed, which lowers the density offluid in the annulus. With this reduction of density of fluids in theannulus, liquid will flow from tubing 26 into annulus 28. Also, thepressure in the formation normally will exceed the pressure in the welland fluids will flow from the formation into the well.

Any one of a number of water-soluble surfactants which have foamproducing properties can be used as the foaming agent. Surface activeagents which have the ability to produce foams include those ofnonionic, anionic and cationic nature. Among the particularly suitablefoaming agents for use in the method of this invention are fatty alkylolamide condensates, substituted polyamines, polyoxyethylene condesates offatty alcohols, polyoxyethylene condensates of fatty acids,polyoxyethylene esters of long chain mixed acids, polyoxyethylene estersof long chain amides, polyoxyethylene condensates of halogenated tallow,polyoxyethylene alkyl phenols, polyoxyethylated polyoxyolefins,polyoxyethylated polyoxyolefin amines, polyoxyethylene aliphatic ethers,polyoxyethylene aliphatic thioethers, phosphoric acid esters ofpolyethylene glycol, condensation products of polyhydric alcohols withwater soluble polybasic acids, alkali metal salts of alkylaryl polyestersulfonates, alkali metal organic sulfates, alkyl alkanoloamine sulfates,alcohol sulfates, alkali metal organic phosphates, fatty acidimidazolines, and the like. Further information concerning such foamingagents and an indication of their commercial availability is given inMcCutcheons Detergent and Emulsifiers Annual, issued yearly.

A particularly preferred foaming agent for use in the method of thisinvention is a commercially available foaming agent which comprises anadmixture of lauryl polyethylene oxide ammonium sulfate and alkanolamidebuilders marketed by Procter and Gamble Company under the trademark0.](. Liquid. Another particularly preferred foaming agent is an alkylpolyethylene oxide sulfate having the formula CIHIZ-I'I z z) M where xis an integer having a value of 8 to ll, y is an integer having a valueof l to 5, and M is sodium, potassium or ammonium. A particularlypreferred alkyl polyethylene oxide sulfate is marketed by GeneralAnaline and Film Corporation under the trademark Alipal CD-l28. Otherparticularly preferred foaming agents are sodium lauryl sulfate,sulfated potassium ricinoleate, sodium alkylnaphthalene sulfonate andehtanolamide fatty acid condensates.

The foaming agent will normallly comprise about 0.01 to 2 percent byweight of the solution in which it is incorporated. Usually about 0.5 to1.5 weight percent foaming agent will produce a satisfactory foam. Theaqueous solution can be formed with fresh water or brine.

It has been found that by employing the method of invention, it ispossible to remove a volume of liquid from a well in a matter of a fewhours, wherein the removal of this volume of fluid by swabbing wouldrequire several days. Wells with exceedingly low formation pressures mayrequire that the process of this invention be repeated to reduce thecolumn of liquid sufficiently that natural flow will occur. However,since the method is inexpensive both in regard to the time and equipmentrequired, this presents no difficulty and wells can be brought toproduction using this method where other methods would be impractical.

This invention is further described by the following example which isillustrative of a specific mode of practicing the invention and is notintended as limiting the scope of the invention as defined by theclaims.

Example 1 This example illustrates the practice of this invention inremoving drilling fluid from an oil well in order to reduce thehydrostatic pressure in the well. The well to be treated is completed inan Artic location at a depth of about 3,200 feet with 5-95 inch diametercasing cemented in place and gun-perforated at about the 3,150 footlevel with two holes per foot throughout a 29 foot potentialoil-producing interval. A 3,]90 foot length of tubing having a 2.36 inchinside diameter and 2.76 inch outside diameter is inserted into thecasing, the lower end of the tubing extending to just below theperforations in the casing. The well is equipped substantially asillustrated in FIG. 6. The tubing and the annular space between thetubing and the sidewall of the casing are filled with drilling fluidhaving a specific gravity of about 1.0.

Only a small compressor of about 147 psig output is available as asource of compressed gas. A surplus length of easing string 11 inches ininternal diameter and about 656 feet long is sealed at each end by metalend pieces thereby converting it to a gas storage vessel having a volumeof about 430 cubic feet. Air from the compressor is admitted into thisgas storage vessel, then water is pumped into the vessel, using a mudcirculation pumpof conventional design, to compress the air in the gasstorage vessel to a pressure of about 2 psig. The air thus compressed isadmittedinto the annulus between the tubing and the casing. In responseto the pressure exerted on the liquid in the annulus by injection ofcompressed air into the annulus, liquid is visually observed to flowfrom the tubing into a surface sump. The air compression and injectionsteps are repeated three times, the air being compressed to about 852psig in each stage. Fluid is visually observed to be displaced from thetubing into the sump at each injection stage. Pressure is maintained onthe annulus during the air injection steps.

Subsequently, about 353 cubic feet of a 1 percent aqueous solution ofOK. Liquid foaming agent is pumped into the annulus. Still more fluid isobserved to be displaced from the tubing.

Pressure on the annulus is relieved, and foam is produced in the annulusreducing the density of the fluid remaining therein. The level of fluidin the well is calculated to be depressed by about 3,116 feet.

Upon completion of the above series of steps, the well is placed onproduction and naturally flows at a relatively high rate.

Various embodiments and modifications of this invention have beendescribed in the foregoing description and draiwngs, and furthermodifications will be apparent to those skilled in the art. Suchmodifications are included within the scope of this invention as definedby the following claims.

Having now described our invention, I claim:

1. A process for initiating production from a well traversing an oiland/or gas bearing formation having insufficient pressure to overcomethe hydrostatic pressure of liquid in the well, said well having atubing extending from the surface downward into the well and havingmeans located at the surface to control flow from the tubing, an annulusbeing formed between said tubing and the wall of the well, and theinterior of the tubing being in fluid communication with the annulus,said process comprising:

injecting at least one slug of compressed gas into the annulus with thetubing open, said slug of gas being of sufficient quantity and atsufficient pressure to displace a portion of the liquid in the annulusfrom the annulus into the tubing and to displace liquid in the tubingupward and out of the well;

with the tubing open and while maintaining the pressure in the annulus,next injecting a solution of a foaming agent into the annulus;thereafter releasing the pressure in the annulus,

thereby generating foam in the annulus; and

allowing fluids to flow from the formation into the well and upwardly tothe surface under formation pressure.

2. The process as defined in claim 1 wherein the compressed gas injectedinto the annulus is air.

3. The process as defined in claim 1 wherein the compressed gas injectedinto the annulus is at a pressure of from about 50 to 1,500 psig.

4. The process as defined in claim 1 wherein the volume of compressedgas injected into the annulus is from about 100 to 3000 cubic feetmeasured at injection temperature and pressure.

5. The process as defined in claim 1 wherein the concentration offoaming agent in said foaming agent solution injected into the annulusis from about 0.0l to about 2 percent by weight.

6. The process as defined in claim 1 wherein the volume of foaming agentsolution injected into the annulus is from about 250 cubic feet to about3,000 cubic feet.

7. The process as defined in claim I wherein a plurality of slugs ofcompressed gas are injected into the annulus prior to the injection ofsaid solution of foaming agent.

8. A process for initiating production from a well traversing an oiland/or gas-bearing formation having insufficient pressure to overcomethe hydrostatic pressure of liquid in the well, said well having atubing extending from the surface downward into the well and havingmeans located at the surfaceto control flow from the tubing, an annulusbeing formed between said tubing and the wall of the well, and theinterior of the tubing being in fluid communication with the annulu saidprocess comprisng:

injecting about 250 to about 3,000 cubic feet of compressed gas measuredat injection conditions of temperature and pressure of about 50 to 1,500psi into the annulus with the tubing open, said injection of compressedgas displacing a portion of the liquid in the annulus from the annulusinto the tubing and displacing liquid in the tubing upward and out ofthe well;

with the tubing open and while maintaining pressure in the annulus, nextinjecting into the annulus, from about 250 to about 3,000 cubic feet ofan aqueous foaming agent solution having a foaming agent concentrationof from about 0.01 to about 2 percent by weight; thereafter releasingthe pressure in the annulus thereby generating foam in the annulus; and

allowing fluids to flow from the formation into the well and upwardly tothe surface under formation pressure.

9. A process for initiating production from a well traversing an oiland/or gas-bearing formation having insufficient pressure in theformation to overcome the hydrostatic pressure of liquid in the well,said well being provided with a tubing extending from the surfacedownward into the well and spaced from the wall of the well, an annulusbeing formed between said tubing and the wall of the well, said tubinghaving means located at the surface to control fow from the tubing, andthe interior of the tubing being in fluid communication with saidannulus, said process comprising:

admitting the output of a low pressure compressor into a gas storagevessel; introducing water into said storage vessel at an elevatedpressure, thereby compressing the gas therein;

injecting at least one slug of the gas so compressed into the annulus ofthe well with the tubing open, thereby displacing a portion of theliquid in the annulus into the tubing and liquid in the tubing up-. wardand out of the well;

with the tubing open and while maintaining pressure in the annulus, nextinjecting an aqueous foaming agent solution into the annulus;

thereafter releasing pressure in the annulus, thereby generating foam inthe annulus, and

allowing fluids toflow from the formation into the well and upwardly tothe surface under formation pressure.

10. A process for initiating production from a well traversing and oiland/or gas-bearing formation having insufficient pressure to overcomethe hydrostatic pressure of liquids in the well, said well beingprovided with a length of tubing extending from the surface downwardinto the well and spaced from the wall of the well, an annulus beingformed between said tubing andthe wall of the well, said tubing having:means located at the surface to control flow from the tubing, and theinterior of said tubing being in fluid communication with the saidannulus, said process comprising:

admitting air at a pressure of about from to 150 psig into a closedair-storage vessel,

introducing sufficient water into said storage vessel to compress theair in said vessel to a pressure of from about 500 psig to'about 1,500psig,

with the tubing open introducing at least one slug of the said air thuscompressed to a pressure of from about 500 psi to about 1,500 psi intothe annulus of the well, the total volume of said gas injected beingfrom about to 3,000 cubic feet measured at injection temperature andpressure, thereby displacing a portion of the liquid in the annulus fromthe annulus into the tubing and displacing liquid in the tubing upwardand out of the well;

with the tubing open and pressure maintained in the annulus, nextinjecting into said annulus from about 250 to about 3,000 cubic feet ofan aqueous foaming agent solution having a foaming agent concentrationof about 0.01 to 2 percent by weight;

thereafter releasing pressure in the annulus, thereby generating foam inthe well, and

allowing fluid to flow from the formation into the well and upwardly tothe surface under formation pl'ESSlll'C

2. The process as defined in claim 1 wherein the compressed gas injectedinto the annulus is air.
 3. The process as defined in claim 1 whereinthe compressed gas injected into the annulus is at a pressure of fromabout 50 to 1, 500 psig.
 4. The process as defined in claim 1 whereinthe volume of compressed gas injected into the annulus is from about 100to 3000 cubic feet measured at injection temperature and pressure. 5.The process as defined in claim 1 wherein the concentration of foamingagent in said foaming agent solution injected into the annulus is fromabout 0.01 to about 2 percent by weight.
 6. The process as defined inclaim 1 wherein the volume of foaming agent solution injected into theannulus is from about 250 cubic feet to about 3,000 cubic feet.
 7. Theprocess as defined in claim 1 wherein a plurality of slugs of compressedgas are injected into the annulus prior to the injection of saidsolution of foaming agent.
 8. A process for initiating production from awell traversing an oil and/or gas-bearing formation having insufficientpressure to overcome the hydrostatic pressure of liquid in the well,said well having a tubing extending from the surface downward into thewell and having means located at the surface to control flow from thetubing, an annulus being formed between said tubing and the wall of thewell, and the interior of the tubing being in fluid communication withthe annulus, said process comprising: injecting about 250 to about 3,000cubic feet of compressed gas measured at injection conditions oftemperature and pressure of about 50 to 1,500 psi into the annulus withthe tubing open, said injection of compressed gas displacing a portionof the liquid in the annulus from the annulus into the tubing anddisplacing liquid in the tubing upward and out of the well; with thetubing open and while maintaining pressure in the annulus, nextinjecting into the annulus, from about 250 to about 3,000 cubic feet ofan aqueous foaming agent solution having a foaming agent concentrationof from about 0.01 to about 2 percent by weight; thereafter releasingthe pressure in the annulus thereby generating foam in the annulus; andallowing fluids to flow from the formation into the well and upwardly tothe surface under formation pressure.
 9. A process for initiatingproduction from a well traversing an oil and/or gas-bearing formationhaving insufficient pressure in the formation to overcome thehydrostatic pressure of liquid in the well, said well being providedwith a tubing extending from the surface downward into the well andspaced from the wall of the well, an annulus being formed between saidtubing and the wall of the well, said tubing having means located at thesurface to control fow from the tubing, and the interior of the tubingbeing in fluid communication with said annulus, said process comprising:admitting the output of a low pressure compressor into a gas storagevessel; introducing water into said storage vessel at an elevatedpressure, thereby compressing the gas therein; injecting at least oneslug of the gas so compressed into the annulus of the well with thetubing open, thereby displacing a portion of the liquid in the annulusinto the tubing and liquid in the tubing upward and out of the well;with the tubing open and while maintaining pressure in the annulus, nextinjecting an aqueous foaming agent solution into the annulus; thereafterreleasing pressure in the annulus, thereby generating foam in theannulus, and allowing fluids to flow from the formation into the welland upwardly to the surface under formation pressure.
 10. A process forinitiating production from a well traversing and oil and/or gas-bearingformation having insufficient pressure to overcome the hydrostaticpressure of liquids in the well, said well being provided with a lengthof tubing extending from the surface downward into the well and spacedfrom the wall of the well, an annulus being formed between said tubingand the wall of the well, said tubing having means located at thesurface to control flow from the tubing, and the interior of said tubingbeing in fluid communication with the said annulus, said processcomprising: admitting air at a pressure of about from 70 to 150 psiginto a closed air-storage vessel, introducing sufficient water into saidstorage vessel to compress the air in said vessel to a pressure of fromabout 500 psig to about 1,500 psig, with the tubing open introducing atleast one slug of the said air thus compressed to a pressure of fromabout 500 psi to about 1,500 psi into the annulus of the well, the totalvolume of said gas injected being from about 100 to 3,000 cubic feetmeasured at injection temperature and pressure, thereby displacing aportion of the liquid in the annulus from the annulus into the tubingand displacing liquid in the tubing upward and out of the well; with thetubing open and pressure maintained in the annulus, next injecting intosaid annulus from about 250 to about 3,000 cubic feet of an aqueousfoaming agent solution having a foaming agent concentration of about0.01 to 2 percent by weight; thereafter releasing pressure in theannulus, thereby generating foam in the well, and allowing fluid to flowfrom the formation into the well and upwardly to the surface underformation pressure.